+1

First step of every design project is to understand the advantages/disadvantages of the choices. Li-Po main advantages are light weight... which is great for portable electronics but does not really matter in a UPS that sits around waiting for a power failure. Li also gives lots of recharge cycles... again does not matter in UPS. Main advantages of lead acid batteries: very cheap for power delivered, delivers high peak currents, long shelf life with proper maintenance. Guess what is ideally suited for UPS service?

Ever hear of an online UPS? The batteries are continually being cycled, not "waiting for a failure".

Mod link to old thread.E
https://forum.allaboutcircuits.com/threads/ups-setup-using-li-ion-batteries.94551/post-1113172

 

I thought that in an online UPS, the batteries are just floating, fully charged, and the inverter is supplied from a big DC power supply.
If I was trying to make a UPS with lithium instead of lead-acid... the easiest solution would be lithium iron phosphate, since the voltages are compatible. Expensive, though less so than I feared: I could put one into my APC UPS for about $200, somewhat more than twice as much as the 12V 12Ah Panasonic SLA that I put in a couple years ago. But the current rating is about half what the UPS needs.
https://www.canbat.com/product/12v-12ah-lithium-battery/

 

I thought that in an online UPS, the batteries are just floating, fully charged, and the inverter is supplied from a big DC power supply.
If I was trying to make a UPS with lithium instead of lead-acid... the easiest solution would be lithium iron phosphate, since the voltages are compatible. Expensive, though less so than I feared: I could put one into my APC UPS for about $200, somewhat more than twice as much as the 12V 12Ah Panasonic SLA that I put in a couple years ago. But the current rating is about half what the UPS needs.
https://www.canbat.com/product/12v-12ah-lithium-battery/

In the system I built the generator/charger shuts off when the batteries are charged, and comes back on when the batteries hit a preset low value. It's a generator backed up solar power system. The inverter is always battery powered.